Project Summary/Abstract The ongoing goal of the Autism Biomarkers Consortium for Clinical Trials (ABC-CT) is to establish electroencephalography (EEG) and eye-tracking (ET) biomarkers that can be used for stratification and/or as sensitive and reliable objective assays related to social function in autism spectrum disorder (ASD) clinical trials. This renewal application seeks to further validate promising measures through three studies designed to enhance and extend the original ABC-CT study: (1) a confirmation study of the original findings in a new cohort using similar design (T1: Baseline, T2: 6 weeks post baseline, T3: 24 weeks post baseline) and sample size/characteristics (200 with ASD, 200 with typical development (TD)); (2) a follow-up study of the original cohort (N=399) to re-administer the biomarker and clinical batteries 2.5-4 years after original ABC-CT enrollment; (3) a feasibility study of parallel EEG and ET biomarkers in preschool-aged (3-5-year-old) children (25 with ASD, 25 with TD). The biomarker and clinical batteries measure key facets of social-communication in ASD using well- validated paradigms appropriate for the intended developmental and cognitive range. The study will rely on the same leadership and five Collaborating Implementation Sites (?Sites?) from the first phase, all highly experienced in multi-site collaborative clinical research using the proposed clinical, EEG, and ET methodologies. The Data Coordinating Core (DCC) will provide a secure informatics infrastructure for communication and data integration across the consortium to ensure organized data management, quality control, and reliable upload to the National Database for Autism Research (NDAR) and NIH Data Repositories. The Administrative Core, in coordination with federal partners in this cooperative agreement, will oversee the operations of the sites, DCC, and Data Acquisition and Analysis Core (DAAC) to ensure methodologically and ethically rigorous, efficient completion of scientific aims. Across all studies, the DAAC will (1) refine and implement the protocols for acquisition and quality control of EEG and ET measures; (2) update and implement rigorous, scientifically valid, and replicable data processing pipelines for EEG and ET biomarker protocols; and (3) implement statistical analyses, provide broad- based statistical consulting services, and spearhead novel methodological development. The DAAC relies upon the team of scientific contributors involved in the first phase and active in collaborative ET, EEG, and statistical methodology development, who are dedicated to the goals of the consortium. DAAC faculty and staff have been selected for specific and unique expertise germane to this project and will put that knowledge toward their specific roles in training, acquisition, processing, and analytics. Productive data flow will be obtained through operations management including facilitating site acquisition, DCC data storage and monitoring, and establishing a clear timeline for DAAC deliverables.